Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

2. For obtaining high COP, the pressure range of compressor should be

Low

Any value

High

Optimum

3. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

4. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

5. The boiling point of ammonia is

-33.3°C

-30°C

-77.7°C

-10.5°C

6. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

7. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

8. The condition of refrigerant after passing through the condenser in a vapour compression system is

Wet vapour

Superheated vapour

Saturated liquid

Dry saturated vapour

9. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

10. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

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11. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Negative

Positive

None of these

12. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

13. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

14. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

40 tons

10 tons

15. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Carnot

Reversed Rankine

16. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

17. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Carnot

Bell Coleman

18. Most thermostatic expansion valves are set for a superheat of

20°C

10°C

5°C

15°C

19. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Always less than unity

Any one of the above

20. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.4

0.6

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21. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

Sub-cooling or under-cooling

None of these

22. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

23. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 9

9: 1

1: 1

24. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

25. A bootstrap air cooling system has

Three heat exchangers

Four heat exchangers

Two heat exchangers

One heat exchanger

26. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

27. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

3.33

2.33

28. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant pressure

Involves no change in volume

Takes place at constant entropy

29. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

30. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

2 bar

8 bar

Page 4 of 4

31. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Axial

Miniature sealed unit

32. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

33. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

34. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

35. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

36. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

37. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Ammonia

Carbon dioxide

Brine

38. The capillary tube, as an expansion device, is used in

Room air conditioners

All of these

Water coolers

Domestic refrigerators

39. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

40. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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